Preheat the broiler to high. Line a baking sheet with a silicone mat or parchment paper.

Heat the oil in a skillet over a medium heat. Add the spinach and cook until it is wilted, stirring regularly. Season with salt and pepper.

Place the tortillas on the baking sheet, and spread the feta over each one. Divide the spinach between the two tortillas. Add the cherry tomatoes and black olives. Finish with some shredded mozzarella.

Place under the broiler and cook until the mozzarella has melted.

Top with two more tortillas, and return to the broiler. Cook until crispy, then carefully flip them over. Cook again until the (now top) tortillas are crispy.

Transfer them to a cutting board and cut each quesadilla into 6 wedges. 

Arrange the wedges on a serving plate, and garnish with the dill.